This invention relates to a surgical apparatus comprising a template and a cooperating drilling means for completing the preparation of a distal femoral surface to accurately receive a femoral component of a posterior-stabilized knee implant prosthesis.
A posterior-stabilized knee prosthesis is indicated for a patient who suffers from an unstable, painful knee joint where the instability is caused by the lack of or inadequacy of the posterior cruciate ligaments. The posterior-stabilized knee implant prosthesis consists of a tibial component with a stabilizing post protruding from the superior surface of the tibial component, a femoral component with an intercondylar stabilizing housing to accept the stabilizing post which provides the stability which the patient's knee joint lacks and typically includes a patella component. The housing on the femoral component is intended to fit snugly within the cancellous bone of the distal femur. For optimum results after implantation, it is very important that the femoral and tibial components of the prosthesis be properly aligned relative to the femur and tibia, respectively, during implantation of the components.
Several two-component posterior-stabilized knee prostheses are presently commercially available. See, for example the HOWMEDICA.RTM. KINEMATIC.TM. Stabilizer Prosthesis from Howmedica, Inc. of Rutherford, N.J. which is described in Brochure No. ST 3210-1 2/81 15M B dated February, 1981 entitled "The Howmedica.RTM. Kinematic.TM. Knee System--Howmedica.RTM. Surgical Techniques". To implant the femoral component of this prosthesis, page 9 of the Brochure indicates that after the distal femoral surface is prepared to produce flat distal femoral surfaces, the KINEMATIC Stabilizer Prosthesis trial femoral component is placed on the distal femur. Using methylene blue dye, the outline of the intercondylar stabilizing housing is marked on the flat surface of the distal femur. A recess for the housing is then made by removing bone from within the marked area using an osteotome. The surgeon is only guided by the blue marking on the flat surface of the distal femur and must try to keep within that area. The surgeon must also estimate the depth to which bone must be removed to enable the housing to be completely received within the recess.
The INSALL/BURSTEIN.TM. Total Knee System from Zimmer USA, Inc. of Warsaw, Ind. is described in Brochure No. 81-038-5230-1004/15MB dated 1981 and entitled "Insall-Burstein.TM. Total Knee System". Page 22 of the brochure describes a Femoral Trimmer instrument (No. 5230-30) which is mounted on the femur to accomplish resection of the anterior and posterior condyles and also contains vertical slots to indicate cuts to the distal femur to create the recess for the trough (stabilizing housing) of the femoral component. Page 24 of that Brochure shows an alignment guide set which contains spacer guides having handles which are used to mark the "approximate" width of the intercondylar groove of the femoral component. Page 25 of that Brochure shows an Intercondylar Trough Gauge (Nos. 5230-40 through 5230-43 for various widths) to provide a means of checking the resected distal femur to assure that the intercondylar notch has been correctly resected to a depth of 20 mm. That page states that the surgeon uses the sizer to make a "visual determination of which area may be improperly resected" if the surgeon observes that the sizer does not fit flush against the resected distal femur. Thus, the surgeon is required to possibly repeatedly resect the bone away from the femur until a proper size recess is created in the distal femur.
Page 17 of Brochure No. 81-038-226-1020/15MZ dated 1981 and entitled "Knee Replacement Using Insall/Burstein Total Condylar Knee System" also from Zimmer USA, Inc. further describes the manner in which a femoral trimmer of the type described in the Howmedica Brochure above is used to create a shallow vertical trough 8 mm deep in the center of the distal femur. Page 17 notes that while the femoral trimmer may be used to determine the width of the notch to be cut to receive the stabilizer housing, the "hole in the femoral shaft may no longer be in the correct position to reinsert the instrument" (due to the cuts made to shape the femur). For this reason, page 17 recommends that a simpler method is to use an alignment guide handle to place marks on the femur and "the marks are subsequently cut to allow for the trough . . . . " It is still up to the surgeon to saw the distal femur to the proper depth and width using the marks as a guide. Even use of the alignment guide only provides cuts which define the width of the recess needed for the housing; the surgeon must resect the bone to the appropriate depth using a saw or an osteotome along with the Intercondylar Trough Gauge to confirm that the appropriate depth has been reached. In another Zimmer USA, Inc. Brochure (No. 84-038- 5230-0172 Rev. 2/5MB dated 1981) entitled "Insall/Burstein.TM. Total Knee System With I/B/F.TM. Total Knee Instrumentation" on pages 31 and 33, still another method is described which employs a template which is used to create a trough across the entire distal femoral surface using a saw and an osteotome.
There still appears to be a need for a surgical apparatus which will accurately and simply provide a snugly-fitting and accurately-aligned recess for the intercondylar stabilizing housing of the femoral component of a posterior-stabilized knee implant prosthesis.